Band offsets and interfacial properties of HfOxNy films grown on Si(1 0 0) through radio-frequency reactive magnetron sputtering were investigated by x-ray photoelectron spectroscopy. The changes in the conduction band offset, the valence band offset, as well as in the interfacial properties were obtained as a function of the annealing temperature. The interfacial layer is unavoidably formed for the deposited films and the composition of the interfacial layer is most likely Hf-silicate and SiOx. With the increase in the annealing temperature, it is confirmed that the reaction between SiOx and HfOxNy films formed more Hf-silicate interfacial layer. The valence band offset (ΔEv) shifts upwards gradually with the increase in annealing temperature due to the decrease in N elements. After thermal treatment, the obtained conduction band offset (ΔEc) increased from 1.20 eV at 500 °C to 1.25 eV at 800 °C.